Our goal is to use genetic methods to define the compounds of the cyclic AMP chemosensory system of Dictyostelium. This sensory system is required for normal gene expression during Dictyostelium differentiation. We will prepare monoclonal antibodies that recognize "differentiation" antigens on the cell surface. Some of these antigens are expected to be components of the cyclic AMP chemosensory system. We will use these monoclonal antibodies to select mutants which have altered differentiation antigens. Such mutants are expected to reveal several functional components of this sensory system. We will construct mutagenic plasmids to obtain mutants by insertional inactivation of genes which are essential for differentiation.